Prosthetic Ankle Joint Mechanism

ABSTRACT

A self-aligning prosthetic foot and ankle assembly has an ankle unit pivotally mounting a foot component. The ankle unit contains a hydraulic piston and cylinder assembly having a piston which is linearly movable within a cylinder. The axis of the cylinder is coincident with a shin axis defined by a shin connection interface on the ankle unit. Bypass passages containing damping resistance control valves provide continuous hydraulic damping of dorsi and plantar ankle flexion, the unit being such that, over the major part of the range of damped movement, there is no resilient biasing in either the dorsi or the plantar direction. This confers a number of advantages, including stabilisation of standing, balance control, and improved stair-walking and ramp-walking.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/051,775, filed Oct. 11, 2013, which is a continuation ofU.S. patent application Ser. No. 11/956,391, filed Dec. 14, 2007, whichclaims the benefit of U.S. Provisional Patent Application No.60/869,959, filed Dec. 14, 2006, each of which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a prosthetic ankle joint mechanism, to a lowerlimb prosthesis comprising a shin component, a foot component, and ajoint mechanism interconnecting the shin and foot components, and to aprosthetic foot and ankle assembly. The joint mechanism is arranged toallow limited damped pivoting movement of the shin component relative tothe foot component.

Current prosthetic foot and ankle systems are generally aligned foroperation as fixed mechanical structures comprising elastic anddeformable elements designed to provide stability during standing andwalking and to return energy for propulsion into the swing phase of thewalking cycle. However, such a device is often uncomfortable for theuser whilst standing and whilst walking on ramps and stairs and walkingat different speeds. Users have also experienced knee instability anddifficulty in maintaining forward motion during roll-over of the footwhile standing and walking on ramps and stairs, with consequentimpairment of efficiency. These difficulties are particularly importantfor transfemoral amputees whose stance phase action is normallycompromised by significantly reduced knee flexion and extension whichwould otherwise assist shock absorption and forwards propulsion duringthe stance phase.

An ankle joint mechanism allowing dynamic hydraulic control of theangular position of a prosthetic foot with respect to a shin componentis disclosed in Mauch Laboratories, Inc., Hydraulik Ankle Unit Manual,March 1988. The shin component is attached to a vane piston housed in afluid-filled chamber with a concave part-circular lower wall. Agravity-controlled ball rolls forwards and backwards on the wallaccording to the orientation of the foot to open or close a bypasspassage in the piston. As a result, dorsi-flexion of the mechanism isprevented when the shin component is vertical, largely irrespective ofwhether the foot is horizontal or inclined downwardly or upwardly. Sucha prosthesis also suffers partly from the disadvantages described above.

Amongst other known prosthetic ankle systems is that of U.S. Pat. No.3,871,032 (Karas). This system contains a damping device having a dualpiston and cylinder assembly with tappet return springs actingcontinuously to return the ankle to a neutral position. EP-A-0948947(O'Byrne) discloses a prosthetic ankle having a ball-and-socket jointwith a chamber filled with a silicone-based hydraulic substance, thejoint having a visco-elastic response. In one embodiment, the chambercontains solid silicone rubber particles suspended in a silicone fluidmatrix. US2004/0236435 (Chen) discloses a hydraulic ankle arrangementwith adjustable hydraulic damping and resilient biasing members mountedanteriorly and posteriorly of an ankle joint rotation axis. InWO00/76429 (Gramtec), a leg prosthesis is described having an anklejoint allowing heel height adjustment by way of a hydraulic piston andlinkage arrangement. Elastic components absorb shock during walking.US2006/0235544 (Iversen et al) discloses a hydraulic ankle mechanismwith a rotary vane.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of this invention, a prosthetic ankle jointmechanism provides a continuously hydraulically damped range of ankleflexion, the mechanism being constructed and arranged such that, over atleast part of said range, the damping resistance is the predominantresistance to flexion. The mechanism preferably comprises a hydrauliclinear piston and cylinder assembly. The piston may have distalconnection means for pivotal connection to a foot component, thecylinder having proximal connection means for connection to a shincomponent. Typically, the piston and cylinder assembly has a centralaxis which is oriented such that when the mechanism is coupled to aprosthetic shin component, the central axis is substantially alignedwith or parallel to a shin axis defined by the shin component.

To allow individual setting of dorsi and plantar-flexion dampingresistances, the mechanism may have a valve arrangement controlling theflow of hydraulic fluid between chambers of the piston and cylinder onopposite sides of the piston, the valve arrangement preferablycomprising first and second adjustable valves for dorsi-flexion andplantar flexion damping control respectively.

According to another aspect of the invention, a prosthetic ankle jointmechanism provides a continuously hydraulically damped range of ankleflexion, the mechanism being constructed and arranged such that, over atleast part of the range, movement in the dorsi and plantar directions issubstantially unbiased resiliently.

The invention also includes a prosthetic foot and ankle assemblycomprising the combination of a foot component and, mounted to the footcomponent, an ankle joint mechanism having the features described above.It is preferred that the ankle joint mechanism includes flexion limitingmeans limiting dorsi flexion of the joint mechanism to a dorsi-flexionlimit, the shin connection interface being arranged to allow connectionof a shin component at different anterior-posterior tilt angles. Theseangles include angles resulting in the shin component having an anteriortilt of at least 3° with respect to the vertical when the jointmechanism is flexed to the dorsi-flexion limit. The dorsi-flexion limitadvantageously corresponds to a predetermined orientation of the shincomponent interface relative to the foot component and may be defined bya mechanical end stop operative by the abutment of one part of theprosthetic foot and ankle assembly associated with the shin componentinterface against another part of the assembly associated with the footcomponent. Conveniently, the end stop is defined by the piston of thepiston and cylinder assembly abutting an end wall of the cylinder.

In the preferred embodiment of the invention described hereinafter, therange of damped ankle flexion is fixed. Nevertheless, theabove-mentioned dorsi-flexion limit may be adjustable over at least arange of anterior-posterior tilt angles from 3° to 6°. In anotherembodiment, the range of damped flexion may alter when the dorsi-flexionlimit is adjusted, but once the adjustment has been made, the range ofdamped flexion is, likewise, fixed from step to step.

The assembly may be arranged such that the relative position of the footcomponent and the shin connection interface at the dorsi-flexion limitis defined independently of the orientation of the assembly in space.

Adjustment of the shin axis orientation in the anterior-posteriordirection with respect to the foot component may be performed using atleast one conventional pyramid alignment interface, preferably the shincomponent interface.

The above-described prosthesis, in which the ankle allows dorsi-plantarflexion over a limited range of movement with largely damped, as opposedto resilient, resistance to motion results in an ankle which is ableeasily to flex under load according to changing activity requirementswithout generation of high reaction moments which would otherwise causediscomfort and compromise the function of the prosthesis. Providingdamped and substantially unbiased movement means that the ankle therebyfunctions in a way such that it remains in its last loaded orientation,having no re-alignment capability once the foot is unloaded. Thisfeature is advantageous to assist foot clearance during the swing phase.

By arranging for the position of the foot component or the footcomponent interface relative to the shin connection interface at thedorsi-flexion limit to be defined independently of the orientation ofthe assembly in space, and by using gravity-independent determination ofthe dorsi-flexion limit, the need for a gravity-dependent valve systemwith an end-stop corresponding to vertical orientation of the shin axisis avoided. The prosthesis described above allows set-up flexibility toalter the dynamics of roll-over through selection of different toespring stiffnesses. The range of yielding motion can be altered byaltering the relative alignment of the foot and shin components.Allowing the shin axis to move to the anterior of the vertical positionis particularly advantageous during stair and ramp walking activities.

The conventional approach of maximising energy storage and return hasproduced designs in which the ankle has a high elastic stiffness at alltimes. Reducing stiffness in the manner proposed in accordance with thepresent invention greatly improves comfort for the user as well ashelping to preserve forwards momentum of the upper body and thuslocomotion efficiency. Reaction moments about the ankle are largelydissipated with the result that voluntary control and proprioception ofthe knee and hip in BK (below-knee) amputees, in particular, isimproved.

According to a further aspect of the invention, there is provided aprosthetic foot and ankle assembly comprising the combination of anankle joint mechanism as described above, together with a prostheticenergy-storing foot which is resiliently deformable to allowdorsi-flexion of at least an anterior portion of the foot relative to anankle-mounting portion of the foot.

The invention also includes a lower limb prosthesis comprising a shincomponent defining a shin axis, a foot component, and an ankle jointmechanism as described above, the ankle joint mechanism coupling theshin component to the foot component, wherein at least one of the footcomponent and the shin component includes a resilient section allowingresilient dorsi-flexion of at least an anterior portion of the footcomponent relative to the shin axis. The foot component may comprise anenergy-storing spring arranged to be deflected when a dorsi-flexion loadis applied to the foot anterior portion. Alternatively, the prosthesismay include a resilient section associated with the coupling of the footcomponent and the ankle joint mechanism, allowing a degree of resilientdorsi-flexion. As another alternative, there may be a resilient sectionassociated with the coupling of the shin component to the ankle jointmechanism.

Another aspect of the invention resides in a prosthetic foot and ankleassembly comprising the combination of an ankle joint mechanism and aprosthetic foot having an anterior portion, a posterior portion and anankle-mounting portion, wherein the assembly constitutes a Maxwell-modeldamper/spring combination of which the damper element is said anklejoint mechanism and the spring element is a spring component arranged inseries with the ankle joint.

Described below is a lower limb prosthesis comprising a shin componentdefining a shin axis, a foot component, and a joint mechanisminterconnecting the shin and foot components and arranged to allowlimited damped pivoting of the shin component relative to the footcomponent about a medial-lateral joint flexion axis during use, whereinthe mechanism comprises: a piston and cylinder assembly the piston ofwhich is movable so as define a variable-volume fluid-filled chamber ofthe assembly, fluid being admitted to or expelled from the chamberthrough at least one damping orifice as the relative orientation of theshin and foot components varies with flexion of the joint mechanism; andflexion limiting means limiting dorsi-flexion of the joint mechanism toa dorsi-flexion limit corresponding to orientation of the shin componentwith the shin axis tilted anteriorly with respect to the vertical by atleast 3 degrees. The joint mechanism is preferably arranged such thatdamped relative pivoting of the shin component and the foot component isallowed over an angular range between dorsi- and plantar-flexion limits,the dorsi-flexion limit being adjustable to different anterior tiltsettings of the shin axis with respect to the foot component. Inparticular, the angular range encompasses a foot-flat,shin-axis-vertical state with the permitted degree of shin axis tiltbeing adjustable to different values to the anterior of the vertical.

In the preferred embodiment of the invention, the joint mechanism has afirst part associated with the shin component and a second partassociated with the foot component, these two parts being pivotallyinterconnected with the connection defining a joint flexion axis. One ofthe two parts includes the chamber of the piston and cylinder assemblyand the other is pivotally connected to the piston, the mechanism beingarranged such that the dorsi-flexion limit is defined by a mechanicalstop limiting relative rotation of the first and second parts. Thismechanical stop may be the abutment of the piston with an end surface ofthe chamber. A cushioning spring or pad may be applied to the topsurface of the piston or to the opposing chamber surface in order toincrease the resistance to dorsi-flexion as the dorsi-flexion limit isapproached.

As for the ability to preset the dorsi-flexion limit, this may befacilitated in a number of ways. For instance, the limit may be set byan adjustable anterior-posterior tilt alignment interface, typicallybetween the joint mechanism and a shin component such as a shin tube.The interface may be of the well-known inverted pyramid construction asdescribed above. Alternatively, the interface may be provided betweenthe joint mechanism and a foot component. Again this may be ofinverted-pyramid construction. Another possibility is a lockable pivotjoint for connecting the foot component to the joint mechanism, havingan adjustment axis running in the medial-lateral direction. As a furtheralternative, an adjustable end stop may be provided in the piston andcylinder assembly, or the connection between the piston and one of thecomponents of the mechanism mounting the foot component or the shincomponent may be adjustable to alter the range of displacement of thepiston in the chamber of the assembly with respect to the angular rangeof movement of the foot component relative to the shin component.

The preferred joint mechanism includes two passages in communicationwith the above-mentioned chamber of the piston and cylinder assembly,each containing a respective non-return valve, one oriented to preventthe flow of fluid from the chamber through its respective passage andthe other oriented to prevent the admission of fluid to the chamberthrough the other passage, so that one permits fluid flow when the jointmechanism is flexing in the direction of dorsi-flexion while the otherpassage permits the flow of fluid when the joint is flexing in thedirection of plantar-flexion. Preferably, both passages have respectiveadjustable-area damping orifices to allow the degree of damping to betuned to the user's requirements.

It is preferred that the piston and cylinder assembly is a hydraulicpiston and cylinder assembly, although it is possible to use a pneumaticassembly.

A locking device may also be provided for locking the joint mechanismagainst pivoting at any of a number of positions of the foot componentrelative to the shin component. Typically this is performed using amanually or electromechanically operated valve which interrupts the flowof fluid to or from the above-mentioned chamber of the piston andcylinder assembly through the bypass passages. The locking devicecomprises a control member having two positions, one in which the jointmechanism operates in a yielding mode and one in which it operates in alocked mode. Retaining means are provided for retaining the controlmember in either of the two positions, e.g. a spring biasing the controlmember into one position and a detent, latch or lock for keeping thecontrol member in the other position.

The invention also includes a prosthetic ankle unit comprising a footconnection interface, a shin connection interface pivotally connected tothe foot connection interface to allow flexion of the unit, a piston andcylinder assembly having a piston that is movable in a fluid-filledchamber of the assembly, the piston being associated with one of theinterfaces and the chamber with the other so that when the shinconnection interface pivots relative to the foot connection interface,the piston moves in the chamber, fluid being admitted to or expelledfrom the chamber through at least one damping orifice according to thedirection of flexion of the unit, wherein the unit further comprisesflexion limiting means limiting dorsi-flexion of the unit to adorsi-flexion limit corresponding to a selected angular position of theinterfaces relative to each other, and wherein at least one of theconnection interfaces is configured to allow anterior-posterior tiltadjustment.

The invention will be described below by way of example with referenceto the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross-section of a foot-ankle prosthesis in accordance withthe invention, including a first ankle unit, sectioned on a centralanterior-posterior (AP) plane;

FIG. 2 is a cross-section of an alternative ankle unit for use in aprosthesis in accordance with the invention, sectioned on an AP in frontof the central AP plane;

FIG. 3 is an anterior elevation of the ankle unit of FIG. 2;

FIG. 4 is a detailed cross-section, taken on a medial-lateral plane, ofthe ankle unit of FIG. 2, showing a locking valve;

FIG. 5 is a diagram illustrating the ankle yielding range afforded by aprosthesis in accordance with the invention; and

FIG. 6 is a diagram illustrating operation of a prosthesis in accordancewith the invention during walking.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, an foot-ankle prosthesis in accordance with theinvention has a foot component 10 with a foot keel 12 comprising a rigidcarrier 12A, and a toe spring 12B and a heel spring 12C which areindependently coupled to the carrier 12A. The keel 12 is a one-piececomponent made from a carbon fibre composite material and is surroundedby a foam cosmetic covering 14.

Mounted to the foot keel 12 is an ankle unit 16 comprising a jointmechanism 18 and a shin connection interface 20. The shin connectioninterface 20 defines a shin connection axis 22. The mounting of theankle unit 16 to the foot keel 12 is by way of an ankle flexion pivot 24defining a flexion axis 24A running in a medial-lateral direction to theanterior of the shin connection axis 22.

The body of the ankle unit 16 forms the cylinder of a piston andcylinder assembly having a piston 28 with upper and lower piston rods28A, 28B, the lower piston rod being pivotally connected to the footkeel 12 at a second pivotal connection 30, this second pivotalconnection defining a second medial-lateral axis which is spaced, inthis case posteriorly, from the flexion axis 24A. It will be seen thatas the body 16 of the ankle unit pivots about the flexion axis 24A, thepiston 28 moves substantially linearly in the cylinder 26.

The cylinder 26 of the piston and cylinder assembly is divided intoupper and lower chambers 26A, 26B. These chambers are linked by twobypass passages in the ankle unit body 16, one of which is visible inFIG. 1 where it is shown by dotted lines since it is behind thesectioning plane of the drawing. The other passage does not appear inFIG. 1 since it is located in front of the sectioning plane. However,its configuration is almost identical, as will be described below. Thesetwo bypass passages communicate with the upper chamber 26A of thecylinder via a locking valve 32, described in more detail below, and acommon linking passage 34 which opens into the upper chamber 26A.

The two bypass passages, one of which, 36, is shown in FIG. 1, eachcontain a damping resistance control valve constituting a manuallyadjustable area orifice 38 and a non-return valve 40. Thisadjustable-area orifice and the non-return valve 40 are arranged inseries in the bypass passage 36 between the locking valve 32 and thelower chamber 26B.

The bypass passage 36 appearing in FIG. 1 has its non-return valve 40oriented to allow the flow of hydraulic fluid from the lower chamber 26Bto the upper chamber 26A. The other bypass passage (not shown) has itsnon-return valve oriented in the opposite direction. Accordingly, one ofthe passages 36 is operative during dorsi-flexion and the other duringplantar-flexion. When the locking valve 32 is open, continuous yieldingmovement of the foot component 10 relative to the ankle unit 16 aboutthe flexion axis 24A is possible between dorsi-flexion andplantar-flexion limits defined by the abutment of the piston with,respectively, the lower wall and the upper wall of the cylinder 26. Thelevel of damping for dorsi-flexion and plantar-flexion is independentlyand manually presetable by the respective adjustable-area orifices.

The shin connection interface 20 is conventional, being of pyramidconstruction. Typically, a tubular shin component is mounted to the shinconnection interface 20, the shin component having, at its distal end,an annular female pyramid receptacle having alignment screws, as wellknown to those skilled in the art, for adjusting the orientation of theshin component relative to the ankle unit 16. At a neutral alignmentposition, the axis of the shin component (the shin axis) is coincidentwith the shin connection axis 22 (shown in FIG. 1). When the shincomponent is affixed to the ankle unit 16 in this neutral position, thelimit of dorsi-flexion of the ankle-foot prosthesis, defined by theabutment of the piston 28 with the lower wall of the cylinder 26corresponds to an anterior tilt of the shin axis relative to thevertical when the user stands on a horizontal surface. The plantarflexion limit, defined by abutment of the piston 28 with the upper wallof the cylinder 26 corresponds to a posterior tilt of the shin axis.

In this embodiment, the anterior and posterior tilt angles of the shinconnection axis 22 at the dorsi-flexion and plantar-flexion limits are 4degrees (anterior) and 8 degrees (posterior) respectively with respectto the vertical.

In this embodiment, the mechanical end-stops represented by the abutmentof the piston 28 with the lower and upper cylinder walls define a yieldrange over which the ankle-foot prosthesis is free to flex duringlocomotion and during standing, providing the locking valve 32 is open.Alteration of the shin component alignment at the shin connectioninterface 20 does not alter the angular magnitude of the yielding rangebecause it is governed by the piston stroke, but it does alter theposition of the limits with respect to the vertical.

It will be understood, therefore, that the angular range magnitude isfixed by the construction and geometry of the ankle-foot prosthesis andits hydraulic joint mechanism. The degrees of dorsi-flexion andplantar-flexion respectively are altered by the alignment of the shincomponent connection, as described above. It will be understood thatalternative alignment interfaces can be used to adjust the positions ofthe dorsi-flexion and plantar-flexion limits. For instance, ananterior-posterior tilt alignment interface may be provided between theankle unit 16 and the foot keel 12. Such an interface is provided by asecond embodiment of the invention, as will now be described withreference to FIGS. 2 and 3.

Referring to FIG. 2, this second embodiment of the invention takes theform of a two-part ankle unit having an ankle unit body 16A which, asbefore, mounts a shin connection interface 20 for adjustable connectionto a shin component (not shown), and a foot mounting component 16B whichincorporates a foot connection interface for receiving a pyramidconnector of the known kind on a foot keel (not shown). The jointmechanism is identical to that described above with reference to FIG. 1with the exception that the flexion and piston rod connection pivots 24,30 are housed in the foot mounting component 16B rather than directly inthe keel of a prosthetic foot. In the case of FIG. 2, the drawing is across-section on a vertical anterior-posterior plane parallel to butspaced from the axis of the shin connection interface 20 and thecylinder 26. Consequently, the bypass passage permitting hydraulic fluidflow from the lower chamber 26B to the upper chamber 26A of the cylinder26 (corresponding to dorsi-flexion, i.e. clockwise rotation of the footmounting component 16B relative to the ankle unit body 16A about thepivot 24) appears in full lines, whereas the common linking passage 34between the control valve 32 and the upper chamber 26A is shown withdotted lines.

It will be understood that the non-return valve 40 has a counterpartnon-return valve in the bypass passage (not shown) allowing for plantarflexion, but that the orientation of that counterpart valve is reversedfrom that shown in FIG. 2, as described above with reference to FIG. 1.

For the avoidance of doubt, it should be pointed out that the bores inthe ankle unit body 16A which house the upper and lower piston rods 28A,28B provide sufficient clearance around the piston rods to allow alimited degree of rocking of the piston 28 and piston rods 28A, 28Brelative to the cylinder as the foot mounting component 16B rotates withrespect to the ankle unit body 16A. The periphery of the piston 28 isshaped so as to have an arcuate cross-section, also for this reason. Thesame features are present in the ankle unit of FIG. 1.

The distal part of the ankle unit body 16A is in the form of a trunnion6AA housing pivot axles of the flexion pivot 24 and the piston rodconnection pivot 30. The foot mounting component 16B has an integralannular female pyramid alignment coupling 16BA. This annular pyramidconnector includes four screws 42, three of which are shown in FIG. 2.

The ankle unit trunnion 6AA is shown more clearly in FIG. 3. Alsovisible in FIG. 3 are two adjustment screws 38A, 38B which areaccessible on the anterior face of the ankle unit body 6A. These formpart of the adjustable-area orifices or flow resistance adjusters, oneof which appears as valve 38 in FIG. 2, and permit manual adjustment ofdamping resistance in the dorsi- and plantar-flexion directionsrespectively.

Referring now to FIG. 4, which is a partial cross-section of the ankleunit on a medial-lateral plane containing the axis of the locking valve32, this locking valve is a spool valve having a spool member 44 whichis slidable in a spool valve bore 46. The bore has three ports. A firstport is that of the common linking passage 34 communicating with theupper chamber 26A of the cylinder 26. Second and third ports 36P, 36Q,offset medially and laterally with respect to the common passage 34,provide for communication with the bypass passages 36 (see FIG. 2).

At one end of the spool member 44, there is a manually operablepushbutton 48, which, when pushed against the outward biasing force of astack 50 of spring washers encircling the spool member within apushbutton housing 52, moves the spool member 44 to its open position,as shown in FIG. 4.

The spool valve bore 46 has three enlarged sections of increaseddiameter in registry, respectively, with the three ports describedabove. The spool member 44 has four full-diameter sections, with sealingrings 54, which are a sliding fit within the bore 46. When the spoolmember 44 is in its open position, as shown in FIG. 4, two of thesefull-diameter sections and their corresponding sealing rings 54 are inregistry with the enlarged sections of the spool valve bore 46, therebyallowing fluid flow between the bypass passage ports 36P, 36Q and thecommon passage 34 communicating with the upper chamber 26A of thecylinder 26. Conversely, when the push button 48 is released, the spoolmember 44 moves to bring the above-mentioned full-diameter portions andtheir respective sealing rings 54 into registry with the non-enlargedsections of the spool valve bore 46 on each side of the port to thecommon passage 34, thereby preventing fluid flow between the uppercylinder chamber 26A and the bypass passage ports 36B, 36Q. It followsthat when the pushbutton 48 is released, the ankle unit is hydraulicallylocked at whichever flexion angle existed at the moment of release. Thepushbutton 48 has a projecting stud 48A which engages a detent recess inthe push button housing 52 when the pushbutton is rotated, allowing thepushbutton to be maintained in its depressed position. This is thenormal position of the spool valve, in which flow of hydraulic fluidthrough the bypass passages is 36 (FIG. 2) is allowed, with the resultthat the ankle unit allows yielding dorsi- and plantar-flexion.

The same locking valve arrangement is present in the ankle unit of thefoot-ankle prosthesis described above with reference to FIG. 1.

Whether the ankle unit is in the form of a two-part assembly fordetachable mounting to a foot component, as described above withreference to FIGS. 2, 3 and 4, or in the form of an ankle unit directlypivotally mounted to a prosthetic foot, as described above withreference to FIG. 1, the joint mechanism allows yielding ankle flexionas shown diagrammatically in FIG. 5. The dotted lines denoteplantar-flexion (PF) and dorsi-flexion (DF) limits of a mechanicalhydraulic yielding range of flexion of a shin component 56 with respectto a foot component 10. The magnitude of the angular range is fixed bythe geometry of the joint mechanism and its damping piston and cylinderassembly. Although in these preferred embodiments, the range magnitudeis fixed, the position of the limits with respect to a neutral positionindicated by the chain lines in FIG. 5 can be altered by adjusting thealignment of the shin component relative to the foot component using oneof the alignable connection interfaces described above. In this way, theflexion range may be biased anteriorly or posteriorly from the positionshown in FIG. 5 to create a larger range of motion in either the PF orDF direction. Typical alignment settings result in a dorsi-flexion limitat 2 degrees to 6 degrees tilt anteriorly with respect to the neutralaxis, dependent on the foot toe spring stiffness in particular, and theplantar flexion limit at 4 degrees to 10 degrees tilt posteriorly withrespect to the neutral axis (shown by the chain lines in FIG. 5).

Providing the manual hydraulic lock is not activated, the unitcontinuously allows yield in the dorsi direction (and plantar direction)up to the preset dorsi-flexion limit during walking and standing.

The applicants have found that providing a yielding ankle with minimal,preferably zero elastic biasing in the dorsi- or plantar directions, andwith flexion limits set within the above ranges, provides advantagesduring stair walking and ramp walking activities, and during standing.In the normal body, the biomechanics of standing balance control arecharacterised by the natural balancing of external moments between jointcentres of rotation. The geometrical position of the joint centres ofrotations and the relative position of the body centre of gravity andthe reaction vector are important for stabilising action. Limb stabilitywith a prosthetic limb is primarily dependent on geometry, notmuscle-induced internal moments. Consequently, standing can be achievedfor long periods with minimal muscular effort. A small amount ofcyclical postural sway of the upper body also helps to create stability.It follows that natural standing posture and balance control can beachieved with joints exhibiting low levels of internal resistive torque,the position of the ground reaction vector relative to the hip, knee andankle joints being the main source of limb stability. Allowing yield ina prosthetic ankle in the manner provided by the ankle-foot prosthesisdescribed above aids this function for a lower limb amputee.

The dynamic action of a lower limb prosthesis having the featuresdescribed above during the stance phase of walking is now described withreference to FIG. 6. At heel strike (a), the ankle is in a dorsi-flexedstate from the roll-over actions of the previous step. As the foot movestowards the flat-foot state (b), the ankle plantar-flexes under theaction of the foot heel spring and hydraulic yield at the ankle. Ingeneral, plantar-flexion at the ankle does not reach the plantar-flexionlimit imposed by the joint mechanism of the prosthesis at this stage.During roll-over (c), the ankle begins to dorsi-flex by way of thehydraulic yield afforded by the prosthesis, providing a smooth roll-overaction, preserving body momentum, and improving knee function. Towardsthe end of the roll-over phase (d), the dorsi-flexion limit imposed bythe joint mechanism is reached. Once this happens, mechanical energy isdirected into the keel of the foot (e) to provide energy return forpush-off. The swing phase is initiated with the foot oriented at thedorsi-flexion end-stop to provide toe clearance during the swing phase.

In summary, the prosthesis described above is an foot-ankle system thatis continuously allowed to yield over a limited range in plantar- anddorsi-flexion. The yielding action is provided by a hydraulic dampercoupled to conventional foot elements (i.e. keel, carrier andindependent carbon fibre composite heel-toe springs). The ankle is,therefore, free to flex continuously over a limited plantar- anddorsi-flexion range via the hydraulic damper with minimal interferencefrom elastic elements during walking and standing. During standing, therelative positions of the hip, knee and ankle joint centres are suchthat substantially normal standing postures can be maintained, themoments about each joint being automatically balanced thereby creatinglimb stability. Moreover, the self-aligning action of the foot-anklesystem facilitates improved control of energy transfer between limbsegments during locomotion, the user's hip joint being the main driverand the knee joint being the main facilitator of mechanical energytransfer. This biomimetic method of stabilisation of standing stabilityand balance control has a further advantage in that, while standing onramps, owing to the yielding action of the hydraulic components, thereare no significant reaction moments generated around the ankle which maycause imbalance between joints and discomfort. Since, owing to thelimited range of hydraulic yielding, the ankle is free to move,adaptation for walking and standing on inclined surfaces and changes tofootwear with various heel heights is achieved automatically. A furtheradvantage of the system is a smoother more progressive transition duringroll-over over a variety of terrains.

Although a pneumatic piston and cylinder assembly can be used in placeof a hydraulic one, the hydraulic variant is preferred,

The preferred construction includes an alignment adaptor to allowsetting and adjustment of the plantar-flexion and dorsi-flexionhydraulic yield limits. Such adjustment allows the prosthetist toprovide for balancing of limb moments during standing.

The degree of resistance to flexion in the dorsi-direction orplantar-direction is manually adjustable (e.g. by rotation of flowcontrol valve elements using a screwdriver). The control valves forcontrolling hydraulic resistance may, in an alternative embodiment, bereplaced by a single adjustable control valve in a common bypasspassage, supplemented, if necessary, by a second control valve in abranch passage.

In addition, the joint provided by the ankle-foot system may behydraulically locked, preferably manually, but also, for instance,remotely in real time using an electrically controlled valve, preferablyoperated wirelessly via a key fob.

The dorsi-flexion end-stop may be cushioned, e.g. by inserting acompression spring on the upper cylinder wall or on the upper face ofthe piston. Alternatively, a resilient elastomeric or felt pad may beprovided on one of these surfaces.

A further variation is the substitution of a hydraulic dorsi-flexion endstop in place of an end-stop determined by abutment of components of thejoint mechanism. In this case the port via which the relevant bypasspassage communicates with the chamber 26B (FIG. 2) of the piston andcylinder assembly may be located in the cylinder side wall of thecylinder above the lower wall of the lower chamber 26B so that as apiston 28 moves with dorsi-flexion of the mechanism, it covers the portthereby preventing further movement. The port may be shaped or dividedinto two or more openings into the chamber so that the resistance todorsi-flexion increases as the dorsi-flexion limit is approached,providing a hydraulic cushion. A similar hydraulic stop may be providedby means of a port in the upper chamber 26A.

In summary, the preferred foot and ankle system as described has alinear piston arrangement for the simple control of a hydraulic dampingrange. There is no need for a pendulum as in some prior artarrangements, nor for electronic control at every step. The dampingrange is set mechanically, the linear piston arrangement being preferredfor simplicity and reliability. Independent dorsi-flexion andplantar-flexion valve adjustment is provided, allowing improved setupand customisation of foot performance to suit the requirements ofindividual amputees. The preferred foot and ankle combination representsa visco-elastic structure according to the Maxwell model, i.e. thedamper of the ankle joint mechanism acts in series with the resilientpart of the foot. The hydraulic damping is active on a step-by-stepbasis, as opposed to being substantially locked on some steps.

1.-37. (canceled)
 38. A prosthetic foot and ankle assembly comprising acombination of: a foot component, and an ankle joint mounted to the footcomponent and having a fixed range of dorsi-plantar flexion duringwalking, wherein a lower end of the ankle joint is pivotally mounted tothe foot component at a pivotal connection about which said fixed rangeof dorsi-plantar flexion occurs, the ankle joint comprising a jointmechanism providing resistance to ankle flexion, wherein the jointmechanism comprises a hydraulic damper providing hydraulic damping andhaving a pair of variable-volume chambers and a valve arrangementcontrolling the flow of hydraulic fluid between said chambers, the valvearrangement comprising first and second adjustable valves, respectivelycomprising first and second orifices each adjustable in area forindependently presetting dorsi-flexion damping resistance andplantar-flexion damping resistance respectively such that during walkingsaid first orifice is preset to provide said hydraulic damping at afirst setting whenever the ankle joint is flexed in a dorsi-flexiondirection and said second orifice is preset to provide hydraulic dampingat a second setting whenever the ankle joint is flexed in aplantar-flexion direction, wherein said joint mechanism includes a firstpassage and a second passage, each passage being in communication witheach of said variable-volume chambers, said first passage containingsaid first adjustable valve and a first non-return valve and said secondpassage containing said second adjustable valve and a second non-returnvalve, said first non-return valve being oriented to prevent the flow offluid between said chambers through said first passage in a firstdirection and said second non-return valve being oriented to prevent theflow of fluid between said chambers through said second passage in asecond direction, wherein the joint mechanism includes a first flexionlimiter that limits dorsi-flexion of the joint mechanism to adorsi-flexion limit and a second flexion limiter that limitsplantar-flexion of the joint mechanism to a plantar-flexion limit,thereby defining said fixed range of dorsi-plantar flexion, and whereinthe fixed range of dorsi-plantar flexion has a magnitude between 6degrees and 16 degrees.
 39. The prosthetic foot and ankle assembly ofclaim 38, wherein the joint mechanism is non-electronically controlledand the hydraulic damping provided by the hydraulic damper isnon-electronically controlled.
 40. The prosthetic foot and ankleassembly of claim 38, having at least one pyramid alignment interfaceallowing adjustment of a shin axis orientation in an anterior-posteriordirection with respect to the foot component.
 41. The prosthetic footand ankle assembly of claim 38, the assembly including a cushioningdevice for increasing resistance to dorsi-flexion as flexion of theankle joint approaches said dorsi-flexion limit.
 42. The prosthetic footand ankle assembly of claim 38, wherein the joint mechanism isconstructed and arranged such that during walking said resistance toankle flexion is predominantly provided by said hydraulic damping in oneor both of the dorsiflexion and the plantar-flexion directions.
 43. Theprosthetic foot and ankle assembly of claim 38, wherein the ankle jointis configured and arranged such that during walking the dorsi-flexionlimit is reached during the stance phase of the gait cycle when walkingon level ground.
 44. The prosthetic foot and ankle assembly of claim 38,further comprising a shin connection interface, wherein the assembly isarranged such that the dorsi-flexion limit corresponds to apredetermined relative orientation of the shin connection interfacerelative to the foot component.
 45. The prosthetic foot and ankleassembly of claim 38, wherein the foot component comprises a resilientlydeformable foot arranged to be deflected when a dorsi-flexion load isapplied to an anterior portion of the foot.
 46. The prosthetic foot andankle assembly of claim 38, wherein the ankle joint is configured andarranged such that the dorsi-flexion limit is between 2 degrees and 6degrees relative to a neutral axis of the assembly, and such that duringwalking the dorsi-flexion limit is reached during the stance phase ofthe gait cycle when walking on level ground.
 47. A prosthetic foot andankle assembly comprising a combination of: a foot component, and anankle joint mounted to the foot component and having a fixed range ofdorsi-plantar flexion during walking, wherein a lower end of the anklejoint is pivotally mounted to the foot component at a pivotal connectionabout which said fixed range of dorsi-plantar flexion occurs, the anklejoint comprising a joint mechanism providing resistance to ankleflexion, wherein the joint mechanism comprises a hydraulic damperproviding hydraulic damping and having a pair of variable-volumechambers and a valve arrangement controlling the flow of hydraulic fluidbetween said chambers, the valve arrangement comprising first and secondadjustable valves, respectively comprising first and second orificeseach adjustable in area for independently presetting dorsi-flexiondamping resistance and plantar-flexion damping resistance respectivelysuch that during walking said first orifice is preset to provide saidhydraulic damping at a first setting whenever the ankle joint is flexedin a dorsi-flexion direction and said second orifice is preset toprovide hydraulic damping at a second setting whenever the ankle jointis flexed in a plantar-flexion direction, wherein said joint mechanismincludes a first passage and a second passage, each passage being incommunication with each of said variable-volume chambers, said firstpassage containing said first adjustable valve and a first non-returnvalve and said second passage containing said second adjustable valveand a second non-return valve, said first non-return valve beingoriented to prevent the flow of fluid between said chambers through saidfirst passage in a first direction and said second non-return valvebeing oriented to prevent the flow of fluid between said chambersthrough said second passage in a second direction, wherein the jointmechanism includes a first flexion limiter that limits dorsi-flexion ofthe joint mechanism to a dorsi-flexion limit and a second flexionlimiter that limits plantar-flexion of the joint mechanism to aplantar-flexion limit, thereby defining said fixed range ofdorsi-plantar flexion, and wherein the hydraulic damping provided by thehydraulic damper is non-electronically controlled, and wherein the footcomponent comprises a resiliently deformable foot, wherein the anklejoint is configured and arranged such that the dorsi-flexion limit isbetween 2 degrees and 6 degrees relative to a neutral axis of theassembly, and such that during walking the dorsi-flexion limit isreached during the stance phase of the gait cycle when walking on levelground.
 48. The prosthetic foot and ankle assembly of claim 47, havingat least one pyramid alignment interface allowing adjustment of a shinaxis orientation in an anterior-posterior direction with respect to thefoot component.
 49. The prosthetic foot and ankle assembly of claim 47,the assembly including a cushioning device for increasing resistance todorsi-flexion as flexion of the ankle joint approaches saiddorsi-flexion limit.
 50. The prosthetic foot and ankle assembly of claim47, wherein the joint mechanism is constructed and arranged such thatduring walking said resistance to ankle flexion is predominantlyprovided by said hydraulic damping in one or both of the dorsi-flexionand the plantar-flexion directions.
 51. The prosthetic foot and ankleassembly of claim 47, further comprising a shin connection interface,wherein the assembly is arranged such that the dorsi-flexion limitcorresponds to a predetermined relative orientation of the shinconnection interface relative to the foot component.
 52. The prostheticfoot and ankle assembly of claim 47, wherein the fixed range ofdorsi-plantar flexion has a magnitude between 6 degrees and 16 degrees.